Light projector



Dec. 31, 1935. GUICHERD LIGHT PROJECTOR Filed May 6', 1933 WM w 2 Wk ,m 6 w "m 6 w m 0 m .u\. QL [m r 1 a g k .N .x a .........x 2% a E E+% :22: u w

Patented Dec. 31, 1935 UNITED STATES FF! CE mrsnr Application May 6, 1933, Serial No. 69,799

In France July 30, 1932 2 Claims.

This invention relates to light projectors, including projectors with total occultation, of the kind which have a mask disposed in front of a reflector for obscuring the lower half thereof and a hood, prolonged towards the front, with edges depending to the horizontal plane passing through the axis of the reflector.

In all the known projectors, it is practically impossible to obtain a luminous beam focussed to a single point. Such a result, in fact, requires a lamp filament having no magnitude and a perfect reflector. In practice even a filament with very low voltage has a relatively considerable bulk and the rays are focussed at several points in a zone about the theoretical focal point; if the reflector is perfectly formed this focal zone almost reproduces the virtual image, very much enlarged, of the filament. Moreover, the vertex of the reflector and all that part of it situated behind the lamp cannot be utilized by reason of the presence of the lamp glass and base. This inefiective area creates a dark zone in the centre of the beam.

The reduction or the total elimination of this dark zone can be obtained either by considerably diminishing the mean angle formed by the beam or by diffusing the beam with the aid of a striated glass. But the first of these known solutions only gives a very reduced angle of utilization for certain applications, particularly for the lighting of crossings-called Code such as imposed in France, for example, by the highway regulations. The second solution has the inconvenience of considerably reducing the luminous intensity. The first solution cannot, moreover, be applied in the case of a projector with total occultation of the kind above indicated, except at the price of an excessive prolongation of the hood.

As regards this latter type of projector a slight displacement of the filament upwards has already been proposed, this method permitting the reduction of the dark zone without requiring an excessively long hood. It would even be possible to completely eliminate this zone by increasing the upward displacement of the filament, but then the plane of occultation would be lowered well below the optical axis and the beam would become dipped and irregular, considerably reducing the utility of the apparatus. It has therefore been necessary up to the present to be content with a compromise consisting in slightly raising the beam and tolerating a part of the dark zone.

The present invention provides an improved light projector having none of the aforesaid disadvantages, permitting nevertheless the partial or total suppression of the dark zone in the centre of the beam. The improvement consists essentially in modifying the curvature of an an- 5 nular part of the reflecting surface adjacent the central ineffective zone, in such manner that the rays reflected by the annular part focus at a relatively greater distance and encroach upon the dark zone. 10 However, when applied to a projector with total occultation of the kind above referred to this modification does not permit the maintenance of an anterior mask descending to the level of the optical axis, for in this case none of 15 the rays intended for the dark zone would arrive at their destination. In projectors of this kind, under a further feature of the invention, the anterior hood is slightly relieved in order to! create between this latter and the lower mask 20 an interstice allowing the passage of horizontal rays reflected by the corrected annular part of the reflector.

The invention will be better understood with aid of the following supplementary description, 25 which refers to the attached diagrammatic drawing, given by way of example only, wherein:

Fig. 1 is a diagrammatic view of the beam of a reflector formed according to the invention;

Fig. 2 is a front view of the reflector shown in 30 Fig. 1;

Fig. 3 is a. side view of a projector with total occultation modified according to the invention;

Fig. 4 is a perspective view of this projector showing a horizontal band of light passing under the relieved anterior mask;

Fig. 5 is a transverse section of the luminous beam reflected by such a projector; and

Fig. 6 is an axial section of a reflector of small dimensions modified according to another arrangement provided by the invention.

In construct-ions previously noted with a reflector having a parabolic section, it is not ordinarily possible to obtain a luminous beam focussed at a theoretical point. The light rays focus at several points in a zone around this theoretical point and reproduce the virtual image of the filament much enlarged. In such constructions, the part of the reflector situated behind the lamp is generally ineffective and creates in the center of the beam a dark zone.

According to the invention this inconvenience is eliminated by modifying the curvature of the reflector (Figs. 1 and 2) in the annular part A adjacent to the ineifective zone in such manner as to divert the rays 1' reflected by this annular part, so that they will be substantially parallel or focus at a very great distance F and encroach upon the dark zone.

While the arrangement shown in Fig. 1 can ordinarily be utilized, no rays could reach the dark zone in the case of a projector with total occultation comprising, as shown in Fig. 3, a mask C obscuring the lower half of the reflector and an anterior hood C with its edges depending to the horizontal plane passing through the optical axis :c-;z:. The edges of anterior hood C' .are therefore relieved to the extent of about one hundredth of the length l of the apparatus. This relieving allows the passage of a horizontal band 1* of rays reflected by the parts of the corrected annulus on both sides of the optical axis (see Fig. 4).

This horizontal band can completely cover the dark zone (see Fig. 5) or the remaining part of this zone if, as may be advantageous, a slight displacement upwards of the lamp L is retained as has been indicated above. In these conditions, the combination of the three features, firstly, a slight displacement of the lamp, secondly, correction of an annular part of the reflector and thirdly, relieving of the anterior hood, permits the obtaining of a regular beam at the cutting off plane without dissipation and without the least dark zone, the interposition of striated glass also being unnecessary.

In the construction of projectors with total occulation as shown in Figs. 3 and 4, the ratio between the diameter D of the reflector and the length I of the apparatus is broadly D/L= For projectors of very small size intended, for example, for the sides of vehicles this proportion obliges the maker to adopt excessively small reflectors of which the efficiency is low. In modifying small reflectors under the invention, the annular part about the central ineifective zone of the reflecting surface is displaced inwardly from a basic curve to form an annular ridge, of which the outer slope merges into the basic curve and the inner slope merges into a surface of lesser focal length. With such a reflector (see Fig. 6) it is advantageous to mount the lamp deeper than usual as indicated at I, so as to utilize a greater part of the light rays with a reflector of unchanged diameter.

I claim:

1. A light projector having a reflector concentrating the rays at a point in front of the projector, a source of light mounted substantially near the optical axis of the reflector, said reflector having an annular zone surrounding its center and reflecting light rays to a point situated at a greater distance in front of the projector than the first mentioned point, an opaque mask covering the lower half of said reflector, with its upper edge located in a horizontal plane passing through the optical axis, and an opaque hood projecting beyond said first mentioned point, coveringthe upper part of the projector and having its lower edge located slightly above the horizontal plane passing through said optical axis.

2. A light projector having a reflector concentrating the rays at a point in front of the projector, a source of light mounted slightly above the optical axis of the reflector, said reflector having an annular zone surrounding its center and reflecting light rays to a point situated at a greater distance in front of the projector than the first mentioned point, an opaque mask covering the lower half of said reflector with its upper edge located in a horizontal plane passing through said optical axis, and an opaque hood projecting beyond said first mentioned point covering the upper part of the projector and having the lower edge located above the horizontal plane passing through said optical axis at a distance approximately equal to one hundredth of the 0 total length of the projector.

LOUIS GUICHERD. 

